1. Technical Field
The invention relates to a puncture sealing agent that is used to seal a punctured tire.
2. Background Art
Various kinds of puncture sealing agents are known as a repairing material that seals a punctured portion, when a puncture hole is caused (for instance, Japanese Patent No. 3210863). In existing puncture sealing agents, mainly, (1) propylene glycol or ethylene glycol as an anti-freezing agent, (2) an additive such as fibers or rubber powder for improving the sealing property and (3) a viscosity improver such as methyl cellulose that suppresses the additive from sedimenting and thereby controls the injecting property are blended in a latex such as NR (natural rubber), NBR (nitrile rubber), SBR (styrene butadiene rubber) or carboxyl-modified NBR.
The additives are different in specific gravity from each other; accordingly, when a third component such as a viscosity improver is added to a latex, the latex flocculates and separates during storage in a vehicle or the like, and furthermore, the separated component (latex and the like) may gelate.
It is thought that this is because (1) when a viscosity improver made of an aqueous polymer such as methyl cellulose or carboxylmethyl cellulose is used, the latex flocculates to form particles of 1 to 100 μm, and (2) a grown particle separates owing to a difference in specific gravity from its surroundings (according to a sedimentation theory described with a formula below, the larger the particle diameter is, the faster the sedimentation (separation) velocity is).
                    υ        =                                            2              ⁢                              (                                  ρ                  -                                      ρ                    0                                                  )                            ⁢                              a                2                                                    9              ⁢                              η                A                                              ⁢          g                                    [                  formula          ⁢                                          ⁢          1                ]            
a: particle diameter, v: sedimentation velocity,
ρ: specific gravity of a particle, ρ0: specific gravity, and
ηA: viscosity coefficient
Namely, it can be said that hardly any effective research has been carried out regarding a puncture sealing agent that can be stably used without causing separation even after long storage while maintaining excellent characteristics such as the puncture hole sealing property and injection stability.